1. Field of the Invention
The present invention relates to the cutting and/or sawing of metal structures. More specifically, the present invention relates to a method and apparatus for diamond wire cutting of complex metal structures, such as nuclear reactor vessels.
2. Related Art
Many complex metal structures, such as nuclear reactor vessels and equipment associated therewith, are required to be quickly and efficiently dismantled during decontamination and  decommissioning projects. The dismantling process requires the cutting of large and complex metal components, which are often radioactive, prior to removal from a site. For example, the Tokamak Fusion Test Reactor (“TFTR”), which ceased operation in April of 1997 and was decommissioned in October of 1999, contained radioactive vacuum vessel portions that were contaminated by prior deuterium-tritium experiments and were required to be removed without exposing workers to hazardous levels of radioactivity. Accordingly, the radiological hazards associated with decommissioning, in addition to the large sizes of such vessels (i.e., 80 cubic meters), present significant challenges.
Methods for dismantling such complex metal structures have been attempted in the past, but none have achieved acceptable results. For example, plasma-arc cutting methods are currently employed in decommissioning projects to cut through metals having thicknesses in excess of 0.5 inches, but require workers to enter the reactor in order to effectuate the cuts and remove equipment. This exposes the workers to potentially unacceptable levels of radioactivity. Further, the workers must be fitted with air-supplied bubble suits prior to entering the vessel. Additionally, airborne radioactive contaminants and harmful gases can be released when the metal structures are cut by the plasma-arc torch, requiring expensive containment, filtration, and respiratory systems to abate such dangers.
Diamond wire cutting methods have been employed for more than 25 years in marble and granite mining operations. Diamond-impregnated beads are affixed to a continuous strand of spring or rubber-encapsulated steel wire that is looped onto a drive pulley and driven at a high speed to cut through stone. This method has proven to be an extremely efficient system for  nondestructive stone extraction and mining operations, and has even been applied to cut concrete support structures and shielding at various nuclear power plant sites. A particular problem with diamond wire cutting of metal structures, however, lies in the inability to efficiently clean and cool the wire as it passes through the metal structure. Further, the wire can easily snag and break on complex metal structures, and can release radioactive components or other projectiles into the air during use.
Accordingly, what would be advantageous, but has not yet been provided, is a method and apparatus for diamond wire cutting of complex metal structures, such as nuclear reactor vessels, that addresses the aforementioned shortcomings. 